AstroNote 2021-156

SN 2020aekp was discovered by Gaia in an observation taken on 2020-12-27 and was also detected by ZTF (Bellm et al. 2019; Graham et al. 2019) and several other time-domain sky surveys.  We initially classified this event as a SN Ia (TNSCR 2021-135) using a low-resolution spectrum taken around maximum light using the SED Machine IFU spectrograph (Blagorodnova et al. 2018, Rigault et al. 2019).  The early evolution of the SN light curve is consistent with Type Ia SNe.  However, the decline of the light curve slows starting about 20 days after peak, eventually flattens, and the light curve is now (~130 days post-discovery) showing a slight rebrightening.

We acquired a second spectrum with the SED Machine on 2021-05-08 which shows strong, asymmetric narrow+intermediate-width emission from H-alpha in addition to a strong calcium-triplet in the NIR and broad iron pseudo-continuum in the blue.  These features are charcteristic of interacting transients and particularly strongly resemble previous SNe of type Ia-CSM (e.g., Silverman et al. 2013).  Unusually, in this case the signs of strong interaction did not develop until well after the initial peak.

The source remains relatively optically bright (~18 mag) and well-positioned for follow-up by ground-based observatories for several more months.

This report is based on observations obtained with the Samuel Oschin Telescope 48-inch and the 60-inch Telescope at the Palomar Observatory as part of the Zwicky Transient Facility project. ZTF is supported by the National Science Foundation under Grant No. AST-2034437 and a collaboration including Caltech, IPAC, the Weizmann Institute for Science, the Oskar Klein Center at Stockholm University, the University of Maryland, Deutsches Elektronen-Synchrotron and Humboldt University, the TANGO Consortium of Taiwan, the University of Wisconsin at Milwaukee, Trinity College Dublin, Lawrence Livermore National Laboratories, and IN2P3, France. Operations are conducted by COO, IPAC, and UW.